Reproducible case for SvelteKit bug: prerendered pages always use Content-Type: text/html, not the content type that was specified in the code.
First, build it for production (bug does not reproduce in dev mode):
$ pnpm install && pnpm build && pnpm preview
Then in your browser, open the Network debug panel.
Then go to http://localhost:4173/atom.xml. Note in the Network panel that the Content-Type
is text/html when i should be application/atom+xml, and there is no Cache-Control
header. Both headers are specified in /src/routes/atom.xml/+server.ts but are being ignored.